Assuming you are not into reloading at this time, I recommend you find a shop that sells reloaded ammo - ask gun guys or call the gun shops listed near you. You should be able to buy bags of 50 reloads or boxes of several hundred rounds for relatively excellent prices - either wadcutters, which are flat across the top of the case (and can give you a crisp, clean hole in the paper target), or 158 gr. round-nose lead. Those will be cheaper than rounds with copper-clad bullets. If you can't find them for $10 or less for 50, then check around for cheap new ammo, also with lead bullets. Prvi Partizan sells for less than $12 for 50.

If you want a very light load - minimal recoil - you can look for reloads that are labeled as "Cowboy" ammo in either 122gr. or 158gr. For your purposes, new factory cowboy ammo would be needlessly expensive.